The present invention relates generally to a chuck, and more particularly to a chuck which is especially suitable for use in hammerdrills and the like.
Many different types of chucks for use in power tools are already known. The purpose of these chucks is to engage a tool bit between the jaws of the chuck, and to hold it so that it can rotate or otherwise move with the spindle of the power tool on which the chuck is mounted. All of these chucks have some type of arrangement which is to prevent the undesired loosening of the jaws from the tool bit, and this is usually done by friction. For example, it is known to provide rubber or other elastomeric elements which are located between and in frictional engagement with the body of the chuck and the turnable sleeve which surrounds the chuck body and which effects the movement of the jaws axially and radially into and out of engagement with the tool bit. The purpose of these elastomeric elements is to create increased friction between the turnable sleeve and the chuck body, so as to prevent undersired turning of the sleeve and thus loosening of the jaws from the tool bit.
In certain applications, however, the prior-art arrangements for preventing loosening are not effective enough. This is particularly true in the case of chucks used in hammerdrills and the like, where the impact energy of a single impact is so great that the prior-art arrangement will not satisfactorily prevent the undesired loosening. Attempts have been made to simply increase the friction exerted by the prior-art arrangements, but it has been found that this makes the operation of the chuck in a sense opening or closing the jaws so difficult that the chuck can in effect be adjusted --to open it or to close it-- only by means of a special key, which is often undersirable.